1. Field of the Invention
The present invention relates to an electric power source apparatus for vehicles having a dynamo and a voltage regulator, and more particularly to such an electric power source apparatus which enables to eliminate high frequency noises generated by making and breaking of relay contact in the voltage regulator.
2. Description of the Prior Art
A dynamo is mounted on a vehicle to charge a vehicle-mounted battery during the rotation of an engine. Since such a dynamo generates a voltage the magnitude of which corresponds to the rotation speed of the engine, the output voltage from the dynamo is regulated by a voltage regulator so that the generated voltage amplitude corresponds to the voltage amplitude of the battery. This regulation is usually carried out in the following manner. The output voltage from the voltage regulator changes in response to the generated voltage of the dynamo, and an exciting current of the dynamo is controlled by the output voltage of the regulator whereby the output voltage of the dynamo is controlled. A contact type voltage regulator and a contactless voltage regulator are known. The former comprises mechanical relays while the latter includes electronic circuits instead of mechanical relays. Because the voltage regulator for vehicles is used in such an adverse environment, it is mostly of contact type. Since the contactless type is expensive to compare with the contact type, the use of the former is limited to a high class car even when it is used for vehicle. One of the problems encountered in the contact type voltage regulator is that switching of the contacts occur frequently in the process of voltage regulation. As a result, high frequency noise components are generated in response to the switching of the contacts and they are passed to a vehicle-mounted FM radio receiver or other communication equipments as noises. Particularly, in an automobile car comprising a defogger wire, a FM-wave receiving antenna is located nearly the deffoger wire and opposite thereto. Practically, the distance between the FM-wave receiving antenna and the defogger wire is of cm order, so that high frequency noises generated in the regulator are easily transmitted to the FM-wave receiving antenna from the deffoger wire by an electromagnetic coupling effect and an electrostatic coupling effect. The noise received by the FM-wave receiving antenna is fed to the FM-radio receiver through a feeder line to defect the FM-radio receiver with the noise. For example, in a vehicle which mounts an FM radio receiver set, the above noises will not a significant problem if the receiving point is very near from the FM transmitting station. However, when the receiving point is distant from the transmitting station, a problem of reduction in S/N ratio arises. In order to eliminate the high frequency noises due to the switching of the contacts of the contact type voltage regulator, several approaches have been proposed. A first approach is to provide a noise absorbing capacitor between a line (line B) connecting the voltage regulator and an output terminal of the dynamo, and a ground point on a chassis. In this approach, there is a disadvantage in that the noises in high frequency region such as 80MHz or higher cannot be eliminated. One of the reasons therefor is that since the chassis is grounded a distributed constant circuit is formed on the chassis, which prevents an inherent object of grounding from being accomplished. The above described effect of the distributed constant circuit appears markedly at the FM frequency band. A second reason is that since there exists non-negligible distance between the line B and the chassis, it is impossible to connect the capacitor directly across the line B and the chassis and hence it must be connected through lines. In the high frequency range such as FM frequency band, the lines themselves exhibit inductive components. Since the inductive components impede the passage of high frequency signal, they sacrifice the inherent function of capacitor, of eliminating high frequency signal or noise. There exists a fixed distance between the line B and the chassis, as stated before, because the relation between the chassis structure and electrical wiring is restricted by the design of various parts and other design matters.
A second approach is to insert a noise eliminating capacitor to a line connected to the line B of the voltage regulator. In this approach, since the capacitor is connected in the voltage regulator, the length of lines connected to the capacitor can be shortened. There are two methods in connecting one end of the capacitor connected to the line B and the opposite end. Firstly, the one end is connected to the chassis, like in the first approach, to operate as chassis ground. In this case, since a distributed constant circuit is formed on the chassis like in the first approach, the noise elimination ability is deteriorated. Secondly, the one end is connected to a line specially provided for grounding. This method can eliminate the drawback encountered in the first method.
However both of the above two methods have a common disadvantage. That is, voltage dividing resistors for selectively passing exciting current to an exciting coil of the dynamo are provided in the voltage regulator. A large current flows through the voltage dividing resistors, which are then heated through power dissipation. Temperature in the voltage regulator rises by the heat generated by the resistors. By this temperature rise the noise eliminating capacitor is directly influenced so that the characteristic of the capacitor changes. In order to avoid the above inconvenience, it may be proposed to use a heat-proof capacitor. However, since such a heat-proof capacitor is expensive and of large size it is not commonly accepted to provide the capacitor in the voltage regulator.